Method for making aqueous solutions of unsaturated quaternary ammonium salts

ABSTRACT

The invention concerns a method for making aqueous solutions of unsaturated quaternary ammonium salts of formula (I) by reacting, in the presence of water, N,N-dimethylaminoethyl acrylate with a quaternizing agent of formula (II): R—Cl, said method is characterized in that it consists in: (a) in a closed reactor containing 5 60 wt. % of N,N-dimethylaminoethyl acrylate required for the reaction and which has been pressurized with air or depleted air at 0.5 to 3 bars, carrying out the reaction by continuously introducing, at a temperature ranging between 35 to 65° C., the quaternizing agent (II), and water, and finally the remaining N,N-dimethylaminoethyl acrylate, until the desired concentration of salt (I) in the water is reached, the water being introduced only when 0–20 wt. % of the amount required for the quaternizing agent (II) reaction has been added; the introduction of the remaining N,N-dimethylaminoethyl acrylate starting only when 20–80 wt. % required for the quaternizing agent (II) reaction has been added; and the pressure at the end of the reaction capable of reaching 9 bars; then (b) in depressurizing while maintaining the oxygen content constant by simultaneous introduction of air and, after returning to atmospheric pressure, eliminating the residual quaternizing agent. In formule (I) and (II). R=methyl or benzyl.

The present invention relates to the manufacture of aqueous solutions ofunsaturated quaternary ammonium salts (hereinafter denoted quaternarysalts) corresponding to the following formula (I):

in which R represents methyl or benzyl,by reaction, in the presence of water, of N,N-dimethyl-aminoethylacrylate (DAMEA) with a quaternizing agent of formula (II):R—Cl (II)in which R is as defined above.

Aqueous solutions of quaternary salts (I) are used to prepare polymersintended to act as cationic flocculents in water treatment.

European patent EP-B-250 325 discloses a process for the preparation ofaqueous solutions of quaternary salts, including those of formula (I)according to which process, in the presence of at least onepolymerization inhibitor:

-   -   in a first stage (a), DAMEA is reacted with 5 to 20% by weight        of the amount by weight of the quaternizing agent necessary for        the reaction or, according to an alternative form (a′), with 5        to 20% by weight, with respect to the weight of the DAMEA, of an        aqueous solution of quaternary salts, which solution comprises        from 50 to 85% by weight of quaternary salts; and    -   in a second stage (b), water and the quaternizing agent are        continuously added until the desired concentration of quaternary        salts in the water is obtained.

During stages (a) and (b), the temperature is maintained at a value ofbetween 30 and 60° C. Furthermore, during stages (a) and (b) and inparticular near the end of the reaction, a stream of oxygenated gas ismaintained in the reaction medium such that the ratio by volume (orvolumetric throughput) of total gas at the outlet of the reactor to thevolume (or volumetric throughput) of oxygen introduced at the inlet ofthis same reactor is less than 100.

This process makes it possible to prepare aqueous solutions ofquaternary salts which have a stability at ambient temperature ofgreater than one year. However, a particularly high content ofimpurities, in particular of

of

and of DAMEA, is found in these solutions. In addition, this processrequires relatively long reaction times, which represents an obviouseconomic disadvantage.

A process intended to reduce the formation of the impurities during thequaternization reaction was then provided in international applicationWO 89/07 588. In accordance with this process, the reaction is carriedout at a temperature of between 10 and 80° C., and

-   (a) in a first stage, all or a portion of the quaternizing agent    necessary for the reaction is introduced into the reactor, this    agent being in the liquid state under the reaction conditions,-   (b) subsequently, the DAMEA is added, and-   (c) as soon as 0 to 30% of the stoichiometry of the DAMEA has been    introduced into the reactor, the remainder of the quaternizing    agent, the remainder of the DAMEA and the water are continuously and    simultaneously added until the desired concentration of quaternary    salts is obtained,-   (d) and, in the case where the quaternizing agent is introduced in    the gaseous state at the reaction temperature, the reaction is    carried out in the presence of oxygen and a pressure is applied so    that the quaternizing agent is liquid at the reaction temperature,    and, at the end of the reaction, the pressure is gradually reduced    to atmospheric pressure and simultaneously a ratio as volumetric    throughput of total gas at the outlet of the reactor to the    volumetric throughput of oxygen introduced into the reactor of less    than 100 is imposed.

The above process according to WO 89/07 588 introduces significantimprovement to the process according to EP-B-250 325. However, ittranspired that the purity with which the quaternary salts are obtainedis still insufficient. Thus, during the reaction of DAMEA with CH₃Cl inaqueous medium, resulting in the salt also denoted subsequently by theabbreviation ADAMQUAT MC, the dimer of ADAMQUAT MC, represented by theformula (1):

is formed as impurities, in addition to acrylic acid (AA), formed byhydrolysis of DAMEA.

By virtue of a series of tests of reactivity with regard topolymerization, it was possible to demonstrate that these impuritiesaffected the quality of the cationic polymers derived from ADAMQUAT.

The applicant company has thus looked for operating conditions for thepreparation of aqueous solutions of the salt of formula (I) which arecapable of minimizing the abovementioned impurities, so as to provide asalt (I) in aqueous solution of very high analytical quality.

This novel process, which thus forms the subject matter of the presentinvention, is characterized in that:

-   (a) the reaction is carried out in a closed reactor, which comprises    5–60% of the amount by weight of DAMEA necessary for the reaction    and which has been pressurized by air or depleted air to 0.5 to 3    bar, by continuously introducing, at a temperature of 35 to 65° C.,    in particular of 40 to 60° C., on the one hand, the quaternizing    agent (II) and, on the other hand, the water and finally the    remaining DAMEA, until the desired concentration of salt (I) in the    water is obtained,    -   the start of the introduction of the water beginning when 0–30%,        in particular 10–20%, of the amount by weight of the        quaternizing agent (II) necessary for the reaction has been        added;    -   the start of the introduction of the remaining DAMEA beginning        when 20–80%, in particular 30–70%, of the amount by weight of        the quaternizing agent (II) necessary for the reaction has been        added; and    -   it being possible for the pressure at the end of the reaction to        reach 9 bar, in particular 4 to 7 bar; then-   (e) the reactor is depressurized while keeping the oxygen content    constant by simultaneous introduction of air and, after returning to    atmospheric pressure, the residual quaternizing agent is removed,    for example by stripping with air.

In accordance with other specific characteristics of the processaccording to the invention:

-   -   the quaternizing agent is introduced over a period of time of        1–7 hours, the water over a period of time of 1–8 hours and the        remaining DAMEA over a period of time of 2–8 hours;    -   the reaction is carried out with a molar ratio of the        quaternizing agent to the DAMEA of 1 to 1.1, preferably of 1 to        1.05;    -   the reaction is carried out with a mean ratio of        water/quaternizing agent throughput of 0.2–1.5, in particular of        0.4–1, a mean ratio of remaining DAMEA/quaternizing agent        throughput of 2.5–5, in particular 3–4, and a mean ratio of        water/remaining DAMEA throughput of 0.2–1.2, in particular of        0.3–0.9.

The process according to the invention makes it possible in particularto prepare aqueous solutions having a concentration of quaternary salts(I) of 50 to 85% by weight and comprising very low amounts ofimpurities, as illustrated in Table 1 below.

Furthermore, the process according to the present invention can becarried out in the presence of at least one stabilizer, which can bechosen from 3,5-di(tert-butyl)-4-hydroxytoluene, hydroquinone methylether, hydroquinone, catechol, tert-butylcatechol, phenothiazine andmixtures of these stabilizers, the content of stabilizing agent(s) beingin particular from 20 to 2000 ppm, preferably from 100 to 1200 ppm, withrespect to the aqueous solution of quaternary salt (I).

In addition, at least one sequestering agent for metals chosen inparticular from diethylene-triaminepentaacetic acid, the pentasodiumsalt of diethylenetriaminepentaacetic acid,N-(hydroxyethyl)-ethylenediaminetriacetic acid and the trisodium salt ofN-(hydroxyethyl)ethylenediaminetriacetic acid can be added to thereaction medium, the content of sequestering agent(s) being inparticular from 1 to 100 ppm, preferably from 5 to 30 ppm, with respectto the aqueous solution of quaternary salt (I).

Generally, the sequestering agents are added in the form of an aqueoussolution as they are generally available in this form. Thus, thepentasodium salt of diethylenetriaminepentaacetic acid sold under thename Versenex 80 is provided in the form of an approximately 40% byweight aqueous solution.

The following examples illustrate the present invention without,however, limiting the scope thereof. From these examples, thepercentages are by weight, unless otherwise indicated.

EXAMPLE 1

200 g of DAMEA (i.e. 46.6% of all the DAMEA) were charged to a 1 ljacketed glass reactor, specially designed to withstand pressure,equipped with a temperature probe, with a gas/liquid specific stirrer(turbine with a hollow shaft), with a valve tared at 10 bar, with abursting disc and with dip pipes for the introduction of the variousreactants. The reactor was closed and then pressurized with 1 bar ofdepleted air. Stirring and heating were begun.

As soon as the temperature reached 40° C. (process temperature=47° C.),the introduction of CH₃Cl was begun at a throughput of 70 g/h. When 35 gof CH₃Cl were introduced, the introduction of water was begun at athroughput of 28.6 g/h. After reacting for 1 h, the CH₃Cl throughput wasbrought back to 20.9 g/h. The introduction of the remainder of the DAMEA(i.e. 229 g) was begun at a throughput of 76.3 g/h after reacting for1.5 h. At the end of the reaction, the reactor was brought back toatmospheric pressure using the following protocol:

-   -   degassing the excess CH₃Cl for 30 minutes with simultaneous        introduction of air into the charge (throughput: 3 Sl/h);    -   gradual return to atmospheric pressure,        and the traces of CH₃Cl were removed by stripping with air        (throughput: 5 Sl/h) for 30 minutes.

The reactor was subsequently cooled and then emptied. 710 g of ADAMQUATMC 80 were recovered and were analyzed by high performance liquidchromatography (HPLC) to determine the contents of AA and of compound(1). The results are reported in Table 1.

The durations of the various phases of the reaction were as follows:

CH₃Cl introduction 5.25 h H₂O introduction 5 h DAMEA introduction 3 hdegassing 0.5 h stripping 0.5 hi.e. a total duration of approximately 6.75 h.

The throughput ratios used were:

H₂O/CH₃Cl 0.41 for the first hour, then 1.37 for the remainder of thereaction; H₂O/DAMEA 0.37 DAMEA/CH₃Cl 3.64.

EXAMPLE 2

The preparation was carried out as in Example 1, except that the CH₃Clthroughput was increased.

The results are also reported in Table 1.

TABLE 1 [Ch₃Cl]/[DAMEA] = 1.05; T = 47° C.; Maximum pressure: 6 bar;DAMEA: 429 g (3 mol); CH₃Cl = 15 g (3.15 mol) Mass of HPLC analysis(ppm) the crude Duration of ADAMQUAT MC reaction introduction H₂O/DAMEA/ H₂O/ dimer of QUATS Example mixture (g) of CH₃Cl (h) DAMEA CH₃ClCH₃Cl AA formula (1)^(*) (%) 1 710 5.25 0.37 3.65 0.4 then 1.37 426 40781 2 724 4 ″ ″ ″ 418 277 82.8 ^(*)Content of ADAMQUAT MC dimer offormula (1), expressed arbitrarily as AA

1. A process for preparing an aqueous solution of unsaturated quaternary ammonium salt of formula I

in which R represents a methyl or benzyl radical, comprising reacting, in the presence of water, N,N-dimethyl-aminoethyl acrylate (DAMEA) with a quaternizing agent of formula II R—Cl (II) in which R is as defined above, wherein: (a) the reaction is carried out in a closed reactor, which comprises 5–60% of the amount by weight of the DAMEA necessary for the reaction and which has been pressurized by air or depleted of air to 0.5 to 3 bar, by continuously introducing, at a temperature of 35 to 65° C., the quaternizing agent of formula (II) and the water and finally the remaining DAMEA, until the desired concentration of the salt of the compound of formula (I) in the water is obtained, wherein the start of the introduction of the water beginning when 0–30% of the amount by weight of the quaternizing agent of formula (II) necessary for the reaction has been added; the start of the introduction of the remaining DAMEA begins when 20–80% of the amount by weight of the quaternizing agent of formula (II) necessary for the reaction has been added; and it being possible for the pressure at the end of the reaction to reach 9 bar; then (b) the reactor is depressurized while keeping the oxygen content constant by simultaneous introduction of air and, after returning to atmospheric pressure, the residual quaternizing agent is removed, and wherein no stabilizer is used in the process as a reagent and optionally a sequestering agent is used as a reagent.
 2. The process as claimed in claim 1, wherein the reaction is carried out at a temperature of 40 to 60° C.
 3. The process as claimed in claim 1, wherein the pressure at the end of the reaction reaches 4 to 7 bar.
 4. The process as claimed in claim 1, wherein the introduction of the water is started when 10–20% of the amount by weight of the quaternizing agent of formula (II) necessary for the reaction has been added.
 5. The process as claimed in claim 1, wherein the introduction of the remaining DAMEA is started when 30–70% of the amount by weight of the quaternizing agent of formula (II) necessary for the reaction has been added.
 6. The process as claimed in claim 1, wherein the quaternizing agent is introduced over a period of time of 1–7 hours, the water over a period of time of 1–8 hours and the remaining DAMEA over a period of time of 2–8 hours.
 7. The process as claimed in claim 1, wherein the reaction is carried out with a molar ratio of the quaternizing agent to the DAMEA of 1 to 1.1.
 8. The process as claimed in claim 1, wherein the reaction is carried out with a mean ratio of water/quaternizing agent throughput of 0.2–1.5; a mean ratio of remaining DAMEA/quaternizing agent throughput of 2.5–5; and a mean ratio of water/remaining DAMEA throughput of 0.2–1.2.
 9. The process as claimed in claim 1, which results in an aqueous solution having a concentration of quaternary salt of formula (I) of 50 to 85% by weight.
 10. The process as claimed in claim 1, carried out in the presence of at least one sequestering agent for metals which is diethylene-triaminepentaacetic acid, the pentasodium salt of diethylenetriaminepentaacetic acid, N-(hydroxyethyl)-ethylenediaminetriacetic acid or the trisodium salt of N-(hydroxyethyl)ethylenediaminetriacetic acid, the content of sequestering agent(s) being 1 to 100 ppm, with respect to the aqueous solution of quaternary salt of formula (I).
 11. The process as claimed in claim 1, wherein the residual quaternizing agent is removed by stripping with air.
 12. The process as claimed in claim 1, wherein the reaction is carried out with a molar ratio of the quaternizing agent to the DAMEA of 1 to 1.05.
 13. The process as claimed in claim 1, carried out in the presence of at least one sequestering agent for metals which is diethylene-triaminepentaacetic acid, the pentasodium salt of diethylenetriaminepentaacetic acid, N-(hydroxyethyl)-ethylenediaminetriacetic acid or the trisodium salt of N-(hydroxyethyl)ethylenediaminetriacetic acid, the content of sequestering agent(s) being 5 to 30 ppm, with respect to the aqueous solution of quaternary salt of formula (I).
 14. The process of claim 1 for preparing an aqueous solution of unsaturated quaternary ammonium salt of formula I

in which R represents a methyl or benzyl radical, comprising reacting, in the presence of water, N,N-dimethyl-aminoethyl acrylate (DAMEA) with a quaternizing agent of formula II R—Cl (II) in which R is as defined above, wherein: (a) the reaction is carried out in a closed reactor, which comprises 5–60% of the amount by weight of the DAMEA necessary for the reaction and which has been pressurized by air or depleted of air to 0.5 to 3 bar, by continuously introducing, at a temperature of 35 to 65° C., the quaternizing agent of formula (II) and the water and finally the remaining DAMEA, until the desired concentration of the salt of the compound of formula (I) in the water is obtained, wherein the start of the introduction of the water beginning when 0–30% of the amount by weight of the quaternizing agent of formula (II) necessary for the reaction has been added; the start of the introduction of the remaining DAMEA begins when 20–80% of the amount by weight of the quaternizing agent of formula (II) necessary for the reaction has been added; and it being possible for the pressure at the end of the reaction to reach 9 bar; then (b) the reactor is depressurized while keeping the oxygen content constant by simultaneous introduction of air and, after returning to atmospheric pressure, the residual quaternizing agent is removed, and wherein no stabilizer and no sequestering agent are used.
 15. The process as claimed in claim 14, wherein the reaction is carried out at a temperature of 40 to 60° C.
 16. The process as claimed in claim 14, wherein the pressure at the end of the reaction reaches 4 to 7 bar.
 17. The process as claimed in claim 14, wherein the introduction of the water is started when 10–20% of the amount by weight of the quaternizing agent of formula (II) necessary for the reaction has been added.
 18. The process as claimed in claim 14, wherein the introduction of the remaining DAMEA is started when 30–70% of the amount by weight of the quaternizing agent of formula (II) necessary for the reaction has been added.
 19. The process as claimed in claim 14, wherein the quaternizing agent is introduced over a period of time of 1–7 hours, the water over a period of time of 1–8 hours and the remaining DAMEA over a period of time of 2–8 hours.
 20. The process as claimed in claim 1, wherein the reaction is carried out with a molar ratio of the quaternizing agent to the DAMEA of 1 to 1.1.
 21. The process as claimed in claim 1, wherein the reaction is carried out with a mean ratio of water/quaternizing agent throughput of 0.2–1.5; a mean ratio of remaining DAMEA/quaternizing agent throughput of 2.5–5; and a mean ratio of water/remaining DAMEA throughput of 0.2–1.2.
 22. The process as claimed in claim 1, which results in an aqueous solution having a concentration of quaternary salt of formula (I) of 50 to 85% by weight.
 23. The process as claimed in claim 1, wherein the reaction is carried out with a molar ratio of the quaternizing agent to the DAMEA of 1 to 1.05. 